The present invention relates to a fiber optic output array and, more particularly, to a two dimensional fiber optic output array adapted to produce high resolution images on a recording surface.
Laser recording systems employing fiber optics to guide light are well known in the art. Output arrays featuring multiple optical sources are frequently used to decrease the total time required to record data. In such systems, the output arrays are normally xe2x80x9cscannedxe2x80x9d in a linear manner relative to a recording surface and the light from each of the optical sources, modulated with input data, records the data onto a xe2x80x9ctrackxe2x80x9d during the scanning pass. In this manner, a single pass of the array writes data onto multiple parallel tracks, thereby reducing the total recording time. The parallel data tracks are often referred to in the art as xe2x80x9craster linesxe2x80x9d. In this application, the two terms, xe2x80x9ctrackxe2x80x9d and xe2x80x9craster linexe2x80x9d are used interchangeably.
With all multi-source output systems, there exists a common hurdle which must be overcome. The physical dimensions of the optical sources can limit the resolution that the system is capable of achieving on the recording surface. The resolution of the raster lines on the recording medium is known as the effective xe2x80x9craster spacingxe2x80x9d or xe2x80x9ctrack spacingxe2x80x9d.
A first technique to reduce the dimensions of the arrays of the optical sources is to use fiber optic cables, which can receive light from the sources and bend it so as to bring the light from individual sources into closer proximity. Many other schemes are presently used to reduce the raster spacing for fiber optic output sources. A common method involves a one dimensional array containing a plurality of fiber optic output sources which are aligned at an angle with respect to the scan direction. This geometry reduces the effective track spacing on the recording surface. Several systems employing this scheme are covered in U.S. Pat. Nos. 4,875,969, 4,923,275, and 5,321,426.
The ""969 patent discloses a linear array of fiber optic output sources which are mounted on a substrate configured with grooves to receive the fiber ends and to precisely space the fibers relative to one another. In addition, to further reduce the spacing of the fiber ends, the cladding of the fiber is etched to decrease its diameter. The ""275 patent discloses a similar apparatus, where the substrate is elongated and includes grooves which narrow in spacing towards the output end, so that upon receiving the fibers, the spacing of the output ends can be narrowed uniformly. Finally, the ""426 patent discloses the use of the ""275 apparatus in a printer head.
As previously mentioned, the common component of the three aforementioned patents is the linear array of fiber optic output sources. The array is oriented at an angle with respect to the scan direction so as to reduce the effective track spacing on the recording medium. This design is depicted in FIG. 1. The array of fiber optic output sources 10 is aligned at an angle xcex8 with respect to the scan direction 12. As a result of this geometry, the images on individual sources 11 are written onto the recording medium such that the effective track spacing a is given by a=d sin xcex8, where d is the actual center to center spacing of the fiber ends. A major drawback associated with the linear array implementation is the limitation imposed by constraints on the field of view of the imaging optics. In order to image an N element array, the field of view of the imaging optics must be at least Nd. The imaging optics, which are located between the tips of the optical fibers and the recording material follow prior art practices such as multi-element lenses with or without autofocus mechanisms. The field of view limitation comes from the imaging option. Therefore, there is a tradeoff between the field of view of the imaging optics and the number of fibers in the array. An associated drawback is the extra step required to etch the cladding from the fibers in the array. The reduction in cladding diameter is helpful to reduce the center to center spacing of the fibers d, which in turn decreases the raster line spacing a and the required field of view Nd of the imaging optics. However, the number of array elements N remains constrained by the required field of view Nd.
U.S. Pat. No. 4,743,091 describes a two dimensional array of optical sources, which substantially reduces the constraint caused by the field of view of the imaging optics. Essentially, the ""091 apparatus is a two dimensional array comprising a combination of one dimensional arrays (similar to those of FIG. 1), that are offset with respect to the adjacent arrays. In this manner, the columns of the array are oriented at an angle with respect to the scanning direction such that a reduction in the effective track spacing is achieved. Having a two dimensional array rather than a one dimensional array effectively reduces the required field of view to approximately {square root over ((2+L N))}d, for the same number N of output sources with a center to center spacing d. The drawback with the ""091 patent is that it is only discloses the use of diodes as optical sources. It does not take advantage of fiber optic technology, which, as mentioned, can bend the light and reduce the center to center spacing of the output elements d.
Finally, U.S. Pat. No. 4,590,492 describes a two dimensional array of fiber optic output sources. The array includes a mask having apertures photolithographically attached to the output ends of the fibers such that there is one aperture positioned over each fiber. The drawback with this arrangement is that a great deal of light energy is lost because of the mask and the system efficiency is substantially reduced. The ""492 invention fails to take advantage of the range of variation in cladding and core diameters of fiber optic lines that are available today.
Accordingly, it is an object of this invention to provide for a two dimensional output array of fiber optic cables which is capable of producing high density raster lines of data on a recording medium.
It is another object of this invention to produce such high density raster lines without being overly constrained by the field of view requirements posed by the imaging optics.
It is a further object of this invention to produce such an output array which maintains maximum light transfer and does not unnecessarily impede light carrying output data from the array. Accordingly, such an apparatus would improve the overall system data recording efficiency.
In accordance with the present invention, a two dimensional fiber optic output array is provided which has a plurality of fibers operative to optically emit modulated data at a high optical efficiency. The array comprises a plurality of columns of fibers and a plurality of rows of fibers.
To reduce the effective track spacing on the recording surface, each one of the rows is offset, in a direction of the rows, relative to the adjacent rows. In this manner, the columns are xe2x80x9ctiltedxe2x80x9d slightly and are oriented at a non-perpendicular angle with respect to the rows.
Each of the fibers in the array has a complete core and cladding and there is no unnecessary attenuation of the output light which would tend to reduce the optical efficiency of the apparatus.
Advantageously, the center to center separation of the fibers in the array may be at least twice the diameter of the fiber core.
In one embodiment of the invention, a spacing element may be used to maintain precise control over the position of the fibers within the rows and columns.
In a second embodiment of the invention, an outside surface of the fiber cladding may be used to maintain precise control over the position of the fibers within the rows and columns. Preferably, with this embodiment, each one of the columns may be offset, in a direction of the columns, relative to the adjacent columns.
Advantageously, the apparatus may use multi-mode fibers or single-mode fibers.